Consider an $n$-player nonzero sum finite game $G$. I have a vague recollection of a wonderful paper proving an equivalence between (1) steady state Nash equilibria of $G$ played countably many times in sequence and (2) a modified form of Nash equilibria that essentially allows enforceable contracts.
For example, the Nash equilibria of the single shot or finitely iterated Prisoner's Dilemma is always defect, but the iterated and cooperative Nash equilibria is always cooperative.
Does anyone remember which paper this might be, or have any hints as to how to find it? I searched for a while but didn't find sufficient keywords.